1. Field of the Invention
This invention concerns the manufacturing method and connectors used by an anisotropic conductive film which has an electrical conductive region in the direction of its thickness, and no conductivity or extremely low conductivity in its lateral direction.
2. Description of the Prior Art
Methods for installing semiconductor devices directly to circuit substrates conventionally include the wire bonding method, the TAB method, the flip chip method, etc., each of which is used in practice. Recently, there have been many proposals for the use of conductive adhesives such as anisotropic conductive films and anisotropic conductive pastes for bonding.
Conventionally, the conductive particles in anisotropic thermoplastic films and thermosetting films are dispersed, or in electrical insulating films metallic protuberances are formed at uniform intervals. Furthermore, there are also anisotropic conductive pastes in which microscopic conductive particles are dispersed in the thermosetting resin. In bonding applications of either anisotropic conductive films or anisotropic conductive pastes, connections are made by means of contact by the conductive particles between the substrate circuits and the semiconductor electrodes. In material where metallic protuberances are formed, a metallic bond is formed by means of metallic alloying between the metallic bulges and the electrodes, thereby making electrical contact.
These prior art approaches do however present certain problems which the instant invention solves.
In the above-mentioned anisotropic conductive film bonding method, conductivity was determined by contact made by the randomly-dispersed metallic particles in the film. The quantity of metallic particles contained in the resin film to create anisotropy, however, was limited. As a result, the number of contact points between the metallic particles becomes fewer, with the drawback of a high contact resistance of 1-10 ohms when anisotropic conductive films were used. Moreover, since a great deal of pressure and heat must be applied to the thermosetting resins and thermoplastic resins in the bond-hardening method for conductor connections, a thermo-compression machine is required.
Furthermore, once the adhesive connections are made, some material remains after reheating to peel off the adhesive. Scraping this material off is inconvenient and repairs present a problem.
In the method where metallic protuberances are formed at regular intervals in insulating films, since there are insulating devices between the regularly-spaced metallic protuberances, there is no need to worry about shorts with the adjacent circuit(s) when conductors are connected. Many contact points are available, and it is thus possible to reduce the connection resistance. However, in order to achieve a stable electrical contact using this method, high temperature heating and pressure are necessary to make alloyed connections between the metal bulge and the semiconductor or substrate electrodes, and so on. This requires special equipment. There is also the problem of damaging the semiconductor devices when put under pressure, as well as breaking circuit connections within the substrate itself. It is also very difficult to repair parts that have been connected according to this method.